1. Field of Invention
The present invention relates to a process and a device for preparing cyclohexanol and cyclohexanone by cyclohexane oxidation.
2. Description of Related Arts
The conventional process for the preparation of cyclohexanol and cyclohexanone comprises: non-catalyticly oxidizing cyclohexane with molecular oxygen to obtain an oxidation mixture containing cyclohexyl hydroperoxide (CHHP) as a main product; decomposing the CHHP to obtain cyclohexanol and cyclohexanone; and rectifying to obtain products of the cyclohexanol and the cyclohexanone. Internationally, the art of catalyticly decomposing the CHHP to obtain the cyclohexanol and the cyclohexanone comprises two manners: the homogeneous catalytic decomposition by bis(tert-butyl) chromate, disclosed by French Rhodia Company; and, the heterogeneous catalytic decomposition by cobalt acetate in the alkaline aqueous solution of sodium hydroxide, disclosed by Dutch DSM.
The homogeneous catalytic decomposition of CHHP by the bis(tert-butyl) chromate has two serious defects. Firstly, during decomposing, the scale formation, mainly the chromium adipate, blocks equipments and pipelines. Disclosed by Rhodia, the phosphoric acid octyl ester is used as the scale inhibitor, which still fails to completely solve the scale formation. The continuous production cycle only lasts for four months; washing and descaling after stalling the production device are executed three times per year. Secondly, the conversion rate is low, wherein the molar conversion rate is only around 92%; and around 5% of the CHHP still remains in the decomposed materials. The remaining CHHP is decomposed under the conditions of a high concentration of cyclohexanol and cyclohexanone, high acidity and a high temperature inside the cyclohexane recycling columns and the cyclohexanol and cyclohexanone product columns, so as to mainly produce acid compounds, like adipic acid, and ester compounds, mainly caprolactone; to speed up the condensation reaction of free radicals of the cyclohexanol and the cyclohexanone, and the esterification reaction of cyclohexanol; and to generate the high-boiling-point substances and reduce the yield. Conventionally, a total molar yield of the worldwide industrial devices adopting the art of the homogeneous catalytic decomposition of CHHP by the bis(tert-butyl) chromate is only around 80%.
The heterogeneous catalytic decomposition by cobalt acetate in the alkaline aqueous solution of sodium hydroxide also has two defects. Firstly, the alkaline decomposition normally compromises with the big secondary reactions, and induces a low decomposition molar yield of only 84%. Secondly, it is difficult to completely separate the cyclohexane oil phase containing cyclohexanol and cyclohexanone from the alkaline aqueous phase containing the alkaline waste. The oil phase always contains a certain amount of the waste alkaline aqueous phase, in such a manner that the scales of the waste alkaline are always formed in the rectification towers subsequently, which blocks the rectification columns and the reboilers thereof, and results in the continuous production cycle of only six months. Conventionally, a total molar yield of the worldwide industrial devices adopting the art of the heterogeneous catalytic decomposition by cobalt acetate in the alkaline aqueous solution of sodium hydroxide is only around 80%.
Conventionally, the worldwide companies respectively adopt one of the above two manners to accomplish decomposing the CHHP at one step. The Chinese patents ZL9411039.9 and ZL98112730.4, filed by the inventor of this application, disclose the two-step alkaline decomposition art. At the first step thereof, the alkalinity is lowered; the recycling amount of the alkaline aqueous phase is increased; the static mixer and the plug flow tower-typed decomposing reactor are used. Industrial application results indicate that, the total molar yield of the device thereof really increases, but the separation of the cyclohexane oil phase from the waste alkaline aqueous phase becomes more difficult. The several sets of industrial production devices of the whole two-step alkaline decomposition art have a molar total yield of around 82%.